CARBOXYLIC ACIDS
AND ESTERS
Page 63 # 3-7
Page 66 # 11,12
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68 Section #1-5
STRUCTURE OF CARBOXYLIC ACIDS
• contain the carboxyl functional group COOH
• the bonds are in a planar arrangement
STRUCTURE OF CARBOXYLIC ACIDS
• contain the carboxyl functional group COOH
• the bonds are in a planar arrangement
• include a carbonyl (C=O) group
and
a hydroxyl (O-H) group
STRUCTURE OF CARBOXYLIC ACIDS
• contain the carboxyl functional group COOH
• the bonds are in a planar (flat) arrangement
• include a carbonyl (C=O) group
a hydroxyl (O-H) group
• are isomers of esters :- RCOOR’
and
HOMOLOGOUS SERIES
Carboxylic acids form a homologous series
HCOOH
CH 3COOH
C 2H 5COOH
HOMOLOGOUS SERIES
Carboxylic acids form a homologous series
HCOOH
CH3COOH
C2H5COOH
With more carbon atoms, there can be structural isomers
C3H7COOH
(CH3)2CHCOOH
NAMING CARBOXYLIC ACIDS
# select the longest chain of C atoms
containing the COOH group
# remove the - e and add - oic acid
# number the chain starting from the end
nearer the COOH group
# side chain positions are based on the C in
COOH being 1
NAMING CARBOXYLIC ACIDS
# e.g. CH3 - CH(CH3) - CH2 - CH2 - COOH
# is called 4-methylpentanoic acid
NAMING CARBOXYLIC ACIDS
METHANOIC ACID
ETHANOIC ACID
PROPANOIC ACID
NAMING CARBOXYLIC ACIDS
BUTANOIC ACID
2-METHYLPROPANOIC ACID
NAMING CARBOXYLIC ACIDS
Many carboxylic acids have trivial names (for
properties or origins)
Formula
Systematic name Trivial name (origin)
HCOOH
methanoic acid
CH3COOH
ethanoic acid
formic acid (latin for ant)
acetic acid (latin for vinegar)
C6H5COOH benzenecarboxylic acid benzoic acid
PHYSICAL PROPERTIES
BOILING POINT
Increases as size increases - due to
increased van der Waals forces
101EC
118EC
141EC
164EC
PHYSICAL PROPERTIES
BOILING POINT
Boiling point is higher for “straight” chain isomers.
VW’s
Forces
164EC
154EC
Greater branching = less surface area contact
=lower inter-molecular forces = lower boiling point
PHYSICAL PROPERTIES
BOILING POINT
Carboxylic acids have high boiling
points for their relative mass
H-Bond Effect for Molecules of Similar Mass
Compound
Ethanoic Acid
1-propanol
Propanal
Butane
Mass
60
60
58
58
BP (C)
118
97
49
- 0.5
Comments
H-bonds form dimers
hydrogen bonding
dipole-dipole
Van der Waals
PHYSICAL PROPERTIES
Unexpectedly high BOILING POINT
Arises from inter-molecular hydrogen bonding due to polar
O—H bonds
HYDROGEN
BONDING
AN EXTREME CASE... DIMERS (2 Molecules “joined”)
• extra inter-molecular attraction = more energy to
separate molecules and higher boiling points
PHYSICAL PROPERTIES
SOLUBILITY
• carboxylic acids are soluble in organic solvents (VW forces
with nonpolar Carbon Chain
• they are also soluble in water due to hydrogen bonding
HYDROGEN
BONDING
PHYSICAL PROPERTIES
SOLUBILITY
• small carboxylic acids dissolve readily in cold
water
• as mass increases, solubility in water decreases
(longer nonpolar carbon chains)
• benzoic acid is fairly insoluble in cold but
soluble in hot water
HYDROGEN
BONDING
PREPARATION OF
CARBOXYLIC ACIDS
Oxidation of aldehydes RCHO
Hydrolysis of esters
+
[O]
RCOOR + H2O
——>
——>
RCOOH
RCOOH + ROH
CHEMICAL
PROPERTIES
ACIDITY
All Organic Acids are weak acids (do not ionize completely)
weak acids RCOOH + H2O(l)
RCOO - (aq)
+ H3O+(aq)
ESTERIFICATION
Reagent(s)
Conditions
Product
Equation
alcohol + acid + strong acid catalyst
(e.g. conc. H2SO4 )
reflux (gentle heating)
ester
Example
H2SO4
CH3OH(l) + CH3COOH(l)
Methanol
ethanoic acid
W
CH3COOCH3(l) + H2O(l)
Methyl ethanoate
ESTERIFICATION
H2SO4
CH3OH(l) + CH3COOH(l)
Methanol
ethanoic acid
W
CH3COOCH3(l) + H2O(l)
Methyl ethanoate
Concentrated H2SO4 is a dehydrating agent
- it removes water causing the equation to
move to the right
ESTERIFICATION
Naming esters from the original alcohol
and carboxylic acid
H2SO4
CH3OH(l) + CH3COOH(l)
Methanol
ethanoic acid
W
CH3COOCH3(l) + H2O(l)
Methyl ethanoate
The alcohol name goes first, drop -ol
and add - yl.
The second word is the name of the
acid -drop -oic acid and add -oate
ESTERS
Structure Substitute an organic group for the H in carboxylic acids
Nomenclature first part from alcohol, second part from acid
e.g. methyl ethanoate CH3COOCH3
To identify the original acid, start at the C=O, move away from the
-O-in the main chain. Include the Carbon of the C=O in the name
of the acid (second word -oate).
The balance of the chain belonged to the alcohol (first word, - yl)
METHYL
ETHANOATE
ETHYL
METHANOATE
ESTERS
Esters are unreactive compared with acids and acyl
chlorides
Esters are structural isomers of carboxylic acids
PROPANOIC ACID
Weak acid
H-bonds result in high solubility in
water, high boiling point, reacts with
alcohols to make esters
METHYL ETHANOATE
Fairly unreactive, insoluble in water,
lower boiling point, hydrolyses to form
acids and alcohols
HYDROLYSIS OF ESTERS
Hydrolysis is the opposite of esterification
ESTER + WATER
WCARBOXYLIC ACID + ALCOHOL
+
ETHYL
METHANOATE
+ H 2O
C2H5OH
ETHANOL
+ HCOOH
METHANOIC
ACID
NATURALLY OCCURING ESTERS
-TRIGLYCERIDES
• component of edible fats and oils
• esters of glycerol (propane-1,2,3-triol)
CH2 OH
CHOH
CH2 OH
Saponification
• hydrolysis of triglycerol esters produces soaps
• a simple soap is the salt of a fatty acid
• most oils contain a mixture of triglycerols, soaps are not
pure
Esters are used as:
! artificial perfumes or scents
! artificial food flavours
! industrial solvents for making cellulose, fats,
paints and varnishes
! solvents in pharmaceutical industries.
! softeners in plastic industries and molding
industries
Natural Esters
Molecule
Propyl ethanoate
Octyl Ethanoate
Isoamyl acetate
Ethyl Butyrate
Flavour
Pear
Orange
Banana
Pineapple
Natural Esters
Molecule
Butyl acetate
Methyl trans-cinnimate
Flavour
Apple
Strawberry
Natural flavours are a vast array of chemical compounds.
Synthetic flavours are simpler.
Artificial Pineapple flavor contains more than 20 ingredients but
ethyl butyrate is the major component.
Isoamyl acetate is also the alarm pheromone for honeybees. Circular esters
are found in oily poisonous secretions of termites.
(Personal.ashland.edu/~bmohney/ket_scholars/esters.html)
Synthetic Esters
Molecule
Plexiglas
Dacron
Benzocaine
Procaine
Use
Long chain ester
Polyester fabric
Pain killer (burns)
Pain killer (burns)
Polyester
Adapted from © JONATHAN HOPTON & KNOCKHARDY PUBLISHING